Venetian blinds have a headrail, a bottom rail and a set of slats carried on ladders that extend from the headrail to the bottom rail. Lift cords extend from the bottom rail through or adjacent the slats and into the headrail. The lift cords may be wound and unwound on an axle within the headrail, but more commonly pass through a cord lock in the headrail and exit the headrail at one end. Conventional cord locks will restrain the lift cords when the blind is in a fully raised, or partially lowered, position. But, typically those cord locks do not lock the cords in place when the blind is fully lowered. Consequently, anyone can grasp a lift cord of a fully lowered blind and pull the lift cord away from the blind until the end of the lift cord, which typically has a tassel, reaches the end of the headrail. When a lift cord is pulled in this way a loop is formed. Children have been known to do this. Indeed, some children have become entangled in a cord loop created in this way and have been strangled. Consequently, the industry has been encouraged to provide safety devices on venetian blinds to prevent cords from being pulled away from the slats. A similar problem can also occur in pleated shades and roman shades.
One solution to this problem that some manufacturers have adopted is to attach a cord stop to each lift cord. One type of cord stop has a donut shape. The lift cord is passed through the center hole and around the body. This type of cord stop is disclosed in U.S. Pat. No. 6,453,971. Another type of cord stop is a ball with a slot that snaps onto the cord. Even though the cord stops that have been used are made from clear plastic, they are quite noticeable and detract from the appearance of the blind. Furthermore, one stop must be attached to each lift cord by the installer after the blind has been mounted on the window. This adds several minutes to the installation of a single blind. Fabricators and installers who install cord stops on their blinds must spend more time on each job thereby increasing the cost of the installation.
There is a need for a mechanism that can be used in venetian blinds and other window coverings that will prevent lift cords from being pulled away from a fully lowered blind. That mechanism should not detract from either the operation or appearance of the blind.
U.S. Pat. No. 5,275,222 discloses a cord lock and release system for blinds having a stationary member and a moveable member between which the lift cords pass. In the preferred embodiments a spring biases the moveable member toward the stationary member to restrain the lift cords. A linkage, which typically is a release cord, is attached to the moveable member. The operator pulls the release cord to move the movable member away from the stationary member to release the lift cords. Since the moveable member is biased to the locked position the cords will normally be restrained. The patent also teaches that a spring is not required and that gravity could keep the moveable member in a locked position. But, without the spring, the moveable member is free to rotate 360° and become stuck in a release position. Even the spring biased system permits rotation of the moveable member through an arc greater than 90°. Another shortcoming of this system is that a single moveable member is provided to restrain all of the lift cords. Lift cords often vary in diameter within a single blind by a few thousandths of an inch. If two lift cords in a blind vary in diameter the movable member in a locked position will restrain the larger diameter cord but may allow the smaller diameter cord to slip past the moveable member. Consequently, there remains a need for a cord lock or other system that will prevent lift cords from being pulled away from a fully lowered blind and not detract from either the operation or appearance of the blind.